In another incident in the same year, Coster became enraged with the victim and grabbed her face and head, banging it repeatedly into a wrought-iron bedhead. At one point, her head became wedged between the bars, and she suffered bruising and abrasions.
In her submissions during sentencing, defence counsel Sarah Saunderson-Warner said a psychological report provided a number of things that could be seen as mitigating, including reduced cognitive abilities because of trauma in his life, which had not previously been spoken about.
She said her client was also extremely remorseful, and had offered to pay $500 reparation to the victim.
Judge Joanna Maze said she had an initial starting point of six and a half years' jail for the sexual violation, uplifted by six months on the other two charges, but she had to take the psychological and cultural reports into account.
Details of the reports were suppressed.
She said the defendant had a history of violence towards women, and the victim was vulnerable, but Coster had indicated "very high levels of remorse".
He was sentenced to three and a half years' prison for the sexual violation, and concurrent terms of six months on each of the other charges. He was ordered to pay $500 reparation to the victim, and had a first strike entered against him.
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334.
• Alternatively contact your local police station.
• If you have been abused, remember it's not your fault.